This invention relates to an optical screen especially suitable for photographic purposes which can continuously change the gradation and exposure range in photosensitive materials.
In general, when objects are photographically recorded, there are required photosensitive materials having a gradation suitable for that object and photographing purposes. For example, when an object is photographed by a camera, a better photograph can be obtained only if a photosensitive material having a relatively soft gradation is used for an object of higher maximum/minimum luminous intensity ratio or if a photosensitive material having a relatively hard gradation is used for an object of lower maxmimum/minimum luminous intensity ratio. Photosensitive materials having various different gradations are therefore provided and utilized as required. However, it is extremely disadvantageous for manufacturers to prepare many kinds of photosensitive materials exactly controlled in various gradations.
For users, furthermore, it is cumbersome and in fact difficult to select optimum photosensitive material for an object and photographing purposes.
Similar problems are found in the so-called printing operation (process) in which photographic papers are printed. In the normal printing operation, negative or positive image is respectively reproduced into positive photographs or duplicates. In order to obtain an ideal print, there is required an ideal combination of an original negative with a photographic paper in gradation. Accordingly, photographic papers and original photographic films such as negative films are produced under severe quality control which is in fact insufficient. Moreover, photographic films and papers which are commercially available are produced by a plurality of manufacturers which are different in design idea and the like. Therefore, it is extremely difficult to obtain constantly an ideal combination of film with photographic paper.
Recently, instant photographic films are being broadly used, so that duplication from the instant photographic films is increasingly required. For this purpose, photographic papers for positive are normally used which are of the same type as one for transparent positive (slide). For better operative efficiency, the same type of photographic paper has been normally used for different operations. However, if a photographic paper designed for slides is used to obtain duplicates from the instant photographic films, prints having very soft tone would be obtained. If a photographic paper suitable for the instant photographic film is used to reproduce prints from slides, the prints will have extremely hard tone. No single photographic paper has been realized in spite of the efforts of many manufacturers.
Furthermore, it is required that a line image such as letters is recorded in one area of a printed photograph. Such a printed photograph includes driving license cards and ID cards in which a photograph of owner's face and letters are simultaneously printed in. It is generally desirable to use photographic papers having relatively hard tone for lined images and to utilize photographic papers having relatively soft tone for face photograph. It is preferred that a photosensitive material is simultaneously provided with harder and softer tone portions. However, no such photosensitive material has been provided from any manufacturer.
Therefore, there is strongly desired a method for regulating the gradation in a photosensitive material from outside to overcome the above problems. In response to this, methods for optically changing the gradation by the use of a photographic screen has been proposed in the "RESEARCH DISCLOSURE" Vols. 175 and 182 respectively issued on Nov., 1978 and June, 1979, at the respective items 17533 and 18276. In these proposed methods, there is used a photographic screen which comprises a light-transmitting (lower transmission density) portion of straight-line, checkerboard or dot pattern and a non-transmitting (higher transmission density) portion. The above "RESEARCH DISCLOSURE" describes that a desired gradation in a color print can be achieved by arranging said screen in front of the exposed side of the color print and exposing the color print through the screen and yet that the gradation in the color print can be changed by using another screen different in the density difference, area ratio, shape or spectral transmission factor difference between the light-transmitting and non-transmitting portions.
In such a manner, photographic images having various different gradations can be obtained by the use of only a single type of photosensitive material. However, a great many types of screens must be provided for the optimum gradation in a photosensitive material. In addition to this, it is cumbersome to choose a screen optimum for an object and photographing purposes from many screens and then exchange that screen for the previous screen in each photographing operation.
It is an object of this invention to provide an optical screen free from such a problem, that is, which can regulate the gradation in photosensitive materials.
Another object of the present invention is to provide a photographic process using such an optical screen.